Fix bitarray ops wrt PCI slots
Fix bitarray ops wrt PCI slots

Introduce new method `_GetFreeSlot()` responsible only for bitarray
operations. It fixes search in case of bitarray is either '0000..'
or '1111..'.

Use it instead of `_UpdatePCISlots()` and in `_GetFreePCISlot()`.

Signed-off-by: Dimitris Aragiorgis <4514117c4a99256e19437c7e3407c4ecbf98aec0@grnet.gr>
Reviewed-by: Jose A. Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>

mbakke/ganeti,apyrgio/snf-ganeti,ganeti/ganeti,yiannist/ganeti,grnet/snf-ganeti,mbakke/ganeti,grnet/snf-ganeti,bitemyapp/ganeti,andir/ganeti,bitemyapp/ganeti,andir/ganeti,yiannist/ganeti,leshchevds/ganeti,yiannist/ganeti,ganeti/ganeti,dimara/ganeti,apyrgio/ganeti,mbakke/ganeti,dimara/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,onponomarev/ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,leshchevds/ganeti,apyrgio/ganeti,apyrgio/snf-ganeti,andir/ganeti