Clean git repo before checkout
Clean git repo before checkout

Sometimes git repo become unusable - it contains a lot of
untracked files. Due to this the following checkout fails
and none of commits processed. The solution is to reset the
state and clean all untracked files.

Change-Id: Id230147ac3bfe739ad8be45a7f87da59807fcea4

0xf2/stackalytics,dliu2015/stackalytics_zanata,mohitsethi/stackalytics,Mirantis/stackalytics,0xf2/stackalytics,0xf2/stackalytics,danielmellado/stackalytics,stackforge/stackalytics,AlexanderYAPPO/stackalytics,mohitsethi/stackalytics,dliu2015/stackalytics_zanata,nihilifer/stackalytics,Code-Fly/stackalytics,mohitsethi/stackalytics,openstack/stackalytics,nihilifer/stackalytics,Mirantis/stackalytics,Code-Fly/stackalytics,Mirantis/stackalytics,nihilifer/stackalytics,mhharsh/stackalytics,openstack/stackalytics,mhharsh/stackalytics,Code-Fly/stackalytics,Solinea/stackalytics,0xf2/stackalytics,AlexanderYAPPO/stackalytics,stackforge/stackalytics,openstack/stackalytics,AlexanderYAPPO/stackalytics,mhharsh/stackalytics,danielmellado/stackalytics,Solinea/stackalytics,Solinea/stackalytics,dliu2015/stackalytics_zanata,openstack/stackalytics,danielmellado/stackalytics,stackforge/stackalytics