py3: encode sys.argv to bytes using .encode()

Differential Revision: https://phab.mercurial-scm.org/D3787

tests/test-import-context.t

@@ -10,7 +10,7 b' Test applying context diffs'
   > fp = open(path, 'wb')
   > for i, pattern in enumerate(patterns):
   >     count = int(pattern[0:-1])
-  >     char = pattern[-1] + '\n'
+  >     char = pattern[-1].encode('utf8') + b'\n'
   >     if not lasteol and i == len(patterns) - 1:
   >         fp.write((char*count)[:-1])
   >     else:

tests/test-patch-offset.t

@@ -8,7 +8,7 b''
   > fp = open(path, 'wb')
   > for pattern in patterns:
   >     count = int(pattern[0:-1])
-  >     char = pattern[-1] + '\n'
+  >     char = pattern[-1].encode('utf8') + b'\n'
   >     fp.write(char*count)
   > fp.close()
   > EOF