Create interface defining strategy of initialization of pkgmgr_installer object

Create interface defining strategy of initialization of pkgmgr_installer object

Smoke tests are randomly crashing since some changes with dbus
connection closing in slp-pkgmgr. It seems to be some time hazard (?)
on closing connection.

Anyway, tests are setting up and closing connection repeatingly.
Introduced interface will allow to customize creation of pkgmgr_installer
object in smoke tests.

Following changes need to be submitted together:
     - https://review.tizen.org/gerrit/59442
     - https://review.tizen.org/gerrit/59443
     - https://review.tizen.org/gerrit/59444

Change-Id: I69f5972c09a593cfe9a282f2120845f85aa65b52