Add EXTRA_BAREMETAL_OPTS to stack.sh

Allow the passing of extra options to the [baremetal] option group
by specifying EXTRA_BAREMETAL_OPTS, using the same format as the
existing flag EXTRA_OPTS.

Change-Id: I209675786c6a33a68d83a371292a1e1749ecb14c
Fix tempest flavors and DEFAULT_INSTANCE_TYPE

The flavor selection was broken if DEFAULT_INSTANCE_TYPE is defined
but not yet created, for example when it is created in local.sh.
This also has the side effect of setting flavor_ref_alt to the first
flavor where it was unset in the previous code.

Change-Id: I1fa48b3f90af45144c92298b6b07a4f7ee3b499f
Correct comment about SWIFT_LOOPBACK_DISK_SIZE.

The comment regarding SWIFT_LOOPBACK_DISK_SIZE in lib/swift used the
incorrect unit (bytes instead of kilobytes).

Change-Id: I86117e36141c0a028a6fa6878a4d540f624e759d
Add .stackenv to gitignore.

Change-Id: I39e91aaf5e9ff29b025fd5a1aa74bad01c5e5bdd
Add stackrc comments to HACKING

Change-Id: I46ff885184a2b5b71caca905c27f28d8b1304011
Merge "Add .stackenv to gitignore."
Merge "Fix tempest flavors and DEFAULT_INSTANCE_TYPE"
Merge "Add EXTRA_BAREMETAL_OPTS to stack.sh"
Merge "Add stackrc comments to HACKING"