Use $() instead of ``

There are other instances of this in other files, just tidying
ceilometer at the moment.

Change-Id: I136a20d7ac50fdf02cbd1102613e324e313b7b0a
XenAPI: Add exit point after JEOS installation

If the user only want to run the installation of Ubuntu - to export the
template as an xva, it just needs to specify a non-empty value for:

EXIT_AFTER_JEOS_INSTALLATION

And the script will exit after the jeos template has been created.

Change-Id: I558e2f2b18ee23c15c7e46e2f7e74543cf26b750
XenAPI: Fix vimrc

DevStack installs a default minimal .vimrc file for the stack user.
Unfortunately the `syntax on` config line is not recognised by the vim
installed in DomU. It results in an annoying message being displayed
whenever the user is using vi. To avoid this issue, removing the `syntax
on` line.

Change-Id: I224465cc3cdba3464ea0a9a751f250ecb6ddc9f3
XenAPI: Always update apt sources

If an appliance is used as a base OS, the user might want to use that in
a different region. With this change we always update the used mirrors
in the template.

Change-Id: I7a119664efac1124e54064311c243c63c2a7944b
Allow multi-line config items in meta-section of local.conf

It would behave such as the contents from each meta-section in
local.conf is copied to the destination files. One exception is the multiline
options not grouped together. In that case, the contents will be grouped
together in its destination config file.

Check tests/test_config.sh for examples.

This was originally committed in https://review.openstack.org/128805.
But the original change used AWK syntax that is not supported in AWK
3.1.8, and caused syntax error on servers with that AWK version. This
patch makes the necessary change so that it's compatible with AWK
3.1.8.

Change-Id: Id1e1fe01f05bd0f19ea6e89c4f4c0f8be695dfce
Partial-Bug: #1374118
Merge "XenAPI: Fix vimrc"
Merge "XenAPI: Add exit point after JEOS installation"
Merge "Allow multi-line config items in meta-section of local.conf"
Merge "XenAPI: Always update apt sources"
Merge "Use $() instead of ``"