Check if volume is bootable when creating an instance

Cinder provides a bootable flags for volumes that's not being
checked when creating an instance.

If a user select a non-bootable volume, then the VM became unusable
since nothing will be booted at all.

This check is done only in case that a volume is selected as root
device for a VM.  Boot from snapshot will still work (even that the
volume will be marked as non-bootable by cinder, but will boot the
attached snapshot instead)
If the attribute bootable is not present, we keep the old behaviour
and allow the instance creation.

Change-Id: I8e028d40d6a11beeac4f043afccb17eb61f6ce62
Closes-Bug: #1321334
Use no_timer_check with soft-qemu

The Linux kernel timer check not working properly
when the hypervisor's thread preempted by the host CPU scheduler.

The timer check is automatically disabled with other types
of hypervisors including the hardware accelerated kvm,
but timer_check is not disabled when qemu used without hardware acceleration.

This issue is frequently mischaracterized as an SSH connectivity issue and
causes rechecks and occasional boot failures.

This change adds no_timer_check kernel parameter when we are using
uec images with qemu.

Closes-Bug: #1312199
Change-Id: I3cfdfe9048fe219fc12cdac8a399b496f237e55e
maint: Fixes wrong docstring of method get_memory_mb_used

Change-Id: Id82b1f9b54ce008650d16a4104e41b80525364f6
Merge "maint: Fixes wrong docstring of method get_memory_mb_used"
Merge "Check if volume is bootable when creating an instance"
Merge "Use no_timer_check with soft-qemu"