webadmin: Adding validation for volume name

The following validations are added for volume name.
- length cannot be more than 50
- name can have only ASCII letters, numbers, '_' or '-' signs

Change-Id: I691c7bbaecb764dcc722fd4d9f3fa7be5018a6d2
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>