Use murano-db-manage to run upgrades

In previous versions of Murano the command used to manage database
was 'murano-manage'. Now it is changed to 'murano-db-manage', however,
'murano-manage' still exists.

This patch fixes the name of the command, and renames variable used to
store path to 'murano-db-manage' to avoid confusion between the two
available commands.

Closes-bug: #1358738

Change-Id: Ib8a7a1f126a15c419dd8b6d27e5dd32bb5196b32
Merge "Use murano-db-manage to run upgrades" into stable/5.0