variables defined matching the regex '[[:alpha:]][[:alnum:]_]*'
(i.e. a single alpha followed by any number of alphanumerics or
underscores). Unfortunately, the code that expends variables inside a
profile does not match this, it incorrectly matched '([[:alpha:]]|_)+'
(one or more alphas or underscores). This patch corrects the behavior
there as well as synchronizing the expected variable names in the
apparmor.d manpage and apparmor.vim syntax file.

It also adds unit tests and testcases to verify the behavior.

Nominated-by: Steve Beattie <sbeattie@ubuntu.com>
Acked-By: John Johansen <john.johansen@canonical.com>