pygrub: trap exception when python module import fails

pygrub: trap exception when python module import fails

Fix the issue when importing 'crypt' module or crypt.crypt fails in
pygrub. The exception is written on the same line like "Failed!"
message but only if there is an exception. If there is no exception,
we don't bother users with details (probably the password they entered
was wrong) so we just display "Failed!" message. Also, the code for
hasPassword() was rewritten not to have try/except block here.

Signed-off-by: Michal Novotny <minovotn@redhat.com>