Remove get_remote_client & check_vm_connectivity methods

As tempest.scenario.manager was announced stable interface in Tempest 27.0.0[1] it can be now reused in plugins.

Replaced methods:
	* get_remote_client
	* check_vm_connectivity

Etherpad concerning this effort:
https://etherpad.opendev.org/p/tempest-scenario-manager-cleanup

[1] https://docs.openstack.org/releasenotes/tempest/v27.0.0.html#release-notes-27-0-0

Change-Id: I41f2a17f924e4f555f176564d365aa7119e1fd5b
6 files changed