powervm: pass on unimplemented aggregate operations

The powervm driver does not implement the add/remove/undo aggregate
operations defined in the base ComputeDriver class which can cause
issues when running Tempest with the powervm driver. This patch simply
overrides the methods in the powervm driver and does a pass like in the
libvirt driver.

Fixes bug 1206528

Change-Id: Ieac227f321339a4069b015303b6e713ab9fad7b7
Fix and Gate on H303 (no wildcard imports)

Wildcard imports make reading code unnecessarily confusing because they
make it harder to see where a functions comes from.  We had two types of
wildcard imports in the code. Unneeded ones in test files that are just
removed, and some that we actually want which are kept using the '#
noqa' comment to tell flake8 to skip specific checks (such as H303)
for that line.

Change-Id: Id4705011579659fd74a4aaa05ac541e9694c483e
Sync config.generator from Oslo

Includes:
7448e7e Fix hostname conflict in config generator

Fixes bug 1205411

Change-Id: I13988ef73db05bbdab355400c19e1ad136b59fc0
Performs hard reboot if libvirt soft reboot raises libvirtError

Currently the libvirt driver will only attempt a hard reboot if a soft
reboot fails and returns False. If a libvirt exception is raised,
however, the hard reboot is not attempted. This patch wraps the soft
reboot in a try block to continue with the hard reboot attempt if a
libvirtError is raised.

Fixes bug 1202974

Change-Id: Ifaff75b33b5123cdd3293e8f263ccb4f72ae726a
Merge "Fix and Gate on H303 (no wildcard imports)"
Merge "Sync config.generator from Oslo"
Merge "Performs hard reboot if libvirt soft reboot raises libvirtError"
Merge "powervm: pass on unimplemented aggregate operations"