Allow useage of server IDs as well as names.

RAX have some hidden images useful for build a xenserver host.
Ensure nodepool can use these by referring to them by image UUID.

Change-Id: Idfefc60e762740f4cffa437933007942a0920970
Support install phase with nodepool

Some operating systems are not available as cloud images. To be able to
create nodes of such operating systems, we must install them first on
top of, or by replacing the standard os. This install phase can
include several automated restarts of the node. This patch adds this
functionality to nodepool, and the ability for nodepool to track the
installation.

New configuration values:
- image.install - specifies a script, that should be executed on the
  standard os. If it's omitted, no installation will be performed.
- image.install-done-stamp - is a path on the instance, whose existence
  is periodically polled by nodepool. The installation is ready, if the
  file exists.
  If this is not specified, the original behavior is reserved - nodepool
  assumes that the host is installed right after the install script
  returned.
- image.install-poll-interval - defaults to 30, specifies the seconds to
  wait between polling for the existence of install_status_file.
- image.install-poll-count - defaults to 10, specifies the number of
  polls nodepool performs before erroring out.

Change-Id: I107c7ada43f5650bfaa81ca99732405e749d158b
Add some logging for ssh_connect

Change-Id: Ib51075ef1364995929c70415de248afc2da03d62
reorder debug statement

Change-Id: I896428a3a94d66c1d8e39c53ab878421d98f0927
Add launch condition

Change-Id: I1e368574c24ce1025ecd07766cff014cbc9372ca
Fix missing parameter

Change-Id: I383a95574a24cbb028a996710236fa3d1cd6fbac
Fix wrong parameter ordering

Change-Id: I76a46d70ab50de7c0e1f5a4fcd1bd66b961eb1c6
Add bigger timeout

Change-Id: Iacdc48ad8557b8462a3e9b56214d98c877425910
Ignore connection errors

Change-Id: I63533b06ba9ec09c5cd9c65477ee115cf6fe2179
Log error message

Change-Id: I95129cda32179f27fb1a3f8a4d2e31e17e72f782
Add more log messages

Change-Id: I15416fa7521bb49fa7d272322722dd6403704ab1
Reduce timeout

Change-Id: Icc4d6f920da1f6d437da2aedd965d6aac03635b2
Configurable timeout before snapshot

Change-Id: If1524324f1942450382c395f5e91b11d2ff20ea9
Merge branch 'npint'

Conflicts:
	nodepool/nodepool.py

Change-Id: I88fb92ee9e909336f28049fd9300c8225c5e4ceb