'Executes nova-manage command for the given action.
:param action: the cli command to run using nova-manage
:type action: string
:param flags: any optional cli flags to use
:type flags: string
:param params: any optional positional args to use
:type params: string
:param fail_ok: if True an exception is not raised when the
cli return code is non-zero
:type fail_ok: boolean
:param merge_stderr: if True the stderr buffer is merged into stdout
:type merge_stderr: boolean'

def nova_manage(self, action, flags='', params='', fail_ok=False, merge_stderr=False):

    return execute('nova-manage', action, flags, params, fail_ok, merge_stderr, self.cli_dir)
