Cast file path to string.

Before passing a path into selinux.matchpathcon, it needs to be casted
to a string, since the path could be unicode and selinux.matchpathcon
does not support unicode.

Closes-Bug: #1260072
SeLinuxGuard: Cast file path to string.

Before passing a path into selinux.matchpathcon, it needs to be casted
to a string, since the path could be unicode and selinux.matchpathcon
does not support unicode.
Azure: minor changes for filename as strings and logging.

We were passing a unicode string to 'runcmd' in the path to the .crt file.
That is because the keyname was coming from ovf file as unicode.
Ie:
  u'/var/lib/waagent/6BE7A7C3C8A8F4B123CCA5D0C2F1BE4CA7B63ED7.crt'

Then, logging was extending not appending errors.