If egrep is not located at /usr/bin/egrep, the os_nova "Get virt type
value and store as var" task will silently fail causing the
nova_virt_type to always default to qemu.
Update the command to include a lookup for the correct path to egrep.
Change-Id: I378b555d157ee3f39d682c3ddadb6e3ffd933503
Closes-Bug: #1531670