Change return value for ValidateMountMode
Change return value for ValidateMountMode

1. rename it from ValidateMountMode to ValidMountMode
Because it's a function simply check mount mode is valid or not.
2. remove the rw check return value
It's not supposed to be combined into this function, and we already
have a function for that check.

Signed-off-by: Qiang Huang <488e06933c295c76472a67dbc6657ac40a756953@huawei.com>

allencloud/cli,allencloud/cli,dnephin/cli,e11137/cli,dnephin/cli,riyazdf/cli,e11137/cli,Zebrilee/cli,cpuguy83/cli,thaJeztah/cli,redpanda/cli,ashfall/cli,thaJeztah/cli,redpanda/cli,Zebrilee/cli,ashfall/cli,docker/cli,cpuguy83/cli,docker/cli,riyazdf/cli