Mer: Revise use of dialogParent() and dialogs modality

Following up 7f229b8 (Mer: Use ICore::dialogParent() for all dialogs)

Use ICore::mainWindow() instead of ICore::dialogParent() for
"spontaneous" message boxes (those not directly related to recent user
actions) and do not show them as modal.

This is to prevent getting unwanted parent-child relations with
"spontaneous" message boxes - see how ICore::dialogParent() is
implemented.

To minimize risks also avoid using ICore::dialogParent() where a
feasible parent is at hand (e.g. "this").

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: Destroy retry-lock-down question box

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Mer: MerConnection: Remove useless m_runner->cancel()

Originally supposed to be in destructor - screwed up during merge.
Actually done implicitly during SshRemoteProcessRunner destruction so
simply removing.

Signed-off-by: Martin Kampas <martin.kampas@jolla.com>
Merge pull request #22 from martyone/next

VM related