Introduce recovery option to pkgmgr_installer

Introduce recovery option to pkgmgr_installer

Pkgmgr declares enum value for recovery installaton
but there is no way for backend to run with this option
as there is missing parsing in pkgmgr_installer_receive_request
which backend is supposed to use.

Adding processing -b option as PKGMGR_REQ_RECOVER in
pkgmgr_installer API.

Note: app-installers backends will expect invocation:
  backend -b /home/guest/apps_rw/recovery-%%%%%%
where file is recovery file generated by interrupted
installation process.

Even the pkgmgr doesn't implements recovery now.
App-installer needs any command line opton to run this mode
when launched from commandline.

Optional parameter of recovery mode is recovery file but if
pkgmgr will support recovery in future, it is supposed that
this may change. This is set in this form for now.

Change-Id: I970607adcb4465e93a84eb774a0d75504cd443d2