Blank lines in vfstab cause exception

A blank line in `/etc/vfstab` will cause:

    invalid output was: Traceback (most recent call last):
      File "/tmp/ansible-tmp-1402370316.9-115108565709265/svr4mount", line 1392, in <module>
        main()
      File "/tmp/ansible-tmp-1402370316.9-115108565709265/svr4mount", line 152, in main
        if mount.entry_exists():
      File "/tmp/ansible-tmp-1402370316.9-115108565709265/svr4mount", line 34, in entry_exists
        if field[0].count('#') > 0:
    IndexError: list index out of range

I was actually managing a fresh install of Solaris 11.1, and there was a blank line at the end of the file.

This PR avoids the exception by skipping blank lines.