Added support for sudo

This patch introduces configure controlled choice of the elevation mechanism
used on the system.

configure has now a new option --with-sudohelper=[usermode|sudo]

Values:
 - usermode: elevation via consolehelper and pam
 - sudo: elevation via sudo

Change-Id: I202c1bbea8c95f5ad12edb4959a7d614c89ea246
Bug-Url: https://bugzilla.redhat.com/1043471
Signed-off-by: Vinzenz Feenstra <vfeenstr@redhat.com>