Improve appmgr UT coverage

Improve existing unit tests coverage for appmgr's 'cm', 'helm' and 'resthooks'
packages.
Fix also 'helm install' command's overwrite configuration '---set' flag to be
'--set'.

Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>
Change-Id: I2a2f13575fc10191c7ee1fe21e8d3ec344cb71cc
9 files changed