build: python 3 compatibility

Ubuntu 16.04 "xenial xerus" does not come with Python 2.x by default.
It is possible to install a python-2.7 package, but this has its own
problem: no `python` or `python2` symlink (see #7717).

This fixes the following scripts to work with python 3:
- `make check` (bctest,py, bitcoin-util-test.py)
- `make translate` (extract_strings_qt.py)
- `make symbols-check` (symbol-check.py)
- `make security-check` (security-check.py)

Explicitly call the python commands using $(PYTHON) instead
of relying on the interpreter line at the top of the scripts.

contrib/devtools/security-check.py

@@ -5,7 +5,7 @@ Exit status will be 0 if successful, and the program will be silent.
 Otherwise the exit status will be 1 and it will log which executables failed which checks.
 Needs `readelf` (for ELF) and `objdump` (for PE).
 '''
-from __future__ import division,print_function
+from __future__ import division,print_function,unicode_literals
 import subprocess
 import sys
 import os
@@ -23,9 +23,9 @@ def check_ELF_PIE(executable):
         raise IOError('Error opening file')
 
     ok = False
-    for line in stdout.split('\n'):
+    for line in stdout.split(b'\n'):
         line = line.split()
-        if len(line)>=2 and line[0] == 'Type:' and line[1] == 'DYN':
+        if len(line)>=2 and line[0] == b'Type:' and line[1] == b'DYN':
             ok = True
     return ok
 
@@ -38,17 +38,17 @@ def get_ELF_program_headers(executable):
     in_headers = False
     count = 0
     headers = []
-    for line in stdout.split('\n'):
-        if line.startswith('Program Headers:'):
+    for line in stdout.split(b'\n'):
+        if line.startswith(b'Program Headers:'):
             in_headers = True
-        if line == '':
+        if line == b'':
             in_headers = False
         if in_headers:
             if count == 1: # header line
-                ofs_typ = line.find('Type')
-                ofs_offset = line.find('Offset')
-                ofs_flags = line.find('Flg')
-                ofs_align = line.find('Align')
+                ofs_typ = line.find(b'Type')
+                ofs_offset = line.find(b'Offset')
+                ofs_flags = line.find(b'Flg')
+                ofs_align = line.find(b'Align')
                 if ofs_typ == -1 or ofs_offset == -1 or ofs_flags == -1 or ofs_align  == -1:
                     raise ValueError('Cannot parse elfread -lW output')
             elif count > 1:
@@ -65,9 +65,9 @@ def check_ELF_NX(executable):
     have_wx = False
     have_gnu_stack = False
     for (typ, flags) in get_ELF_program_headers(executable):
-        if typ == 'GNU_STACK':
+        if typ == b'GNU_STACK':
             have_gnu_stack = True
-        if 'W' in flags and 'E' in flags: # section is both writable and executable
+        if b'W' in flags and b'E' in flags: # section is both writable and executable
             have_wx = True
     return have_gnu_stack and not have_wx
 
@@ -84,7 +84,7 @@ def check_ELF_RELRO(executable):
         # However, the dynamic linker need to write to this area so these are RW.
         # Glibc itself takes care of mprotecting this area R after relocations are finished.
         # See also http://permalink.gmane.org/gmane.comp.gnu.binutils/71347
-        if typ == 'GNU_RELRO':
+        if typ == b'GNU_RELRO':
             have_gnu_relro = True
 
     have_bindnow = False
@@ -92,9 +92,9 @@ def check_ELF_RELRO(executable):
     (stdout, stderr) = p.communicate()
     if p.returncode:
         raise IOError('Error opening file')
-    for line in stdout.split('\n'):
+    for line in stdout.split(b'\n'):
         tokens = line.split()
-        if len(tokens)>1 and tokens[1] == '(BIND_NOW)' or (len(tokens)>2 and tokens[1] == '(FLAGS)' and 'BIND_NOW' in tokens[2]):
+        if len(tokens)>1 and tokens[1] == b'(BIND_NOW)' or (len(tokens)>2 and tokens[1] == b'(FLAGS)' and b'BIND_NOW' in tokens[2]):
             have_bindnow = True
     return have_gnu_relro and have_bindnow
 
@@ -107,8 +107,8 @@ def check_ELF_Canary(executable):
     if p.returncode:
         raise IOError('Error opening file')
     ok = False
-    for line in stdout.split('\n'):
-        if '__stack_chk_fail' in line:
+    for line in stdout.split(b'\n'):
+        if b'__stack_chk_fail' in line:
             ok = True
     return ok