vdsClient: alternative ways to provide password

Current method to provide password for vdsClient commands is typing it
in the command line. The BZ1032525 requests to provide safer way.

The patch implements new alternatives to provide command's password
value instead of a plain text.

This change introduces an new field, 'auth=', usage:
 * auth=[alt:value] with following posibilities:
 ** auth=file:path - read password from the first line of the file
                     pointed by path
 ** auth=env:name - read password from the environment variable 'name'
 ** auth=pass:password - use plaintext password, provided in case would
                         want to depricate the old format altogether.

This change affects the following commands:
Group 1:
 * connectStorageServer
 * disconnectStorageServer
 * validateStorageServerConnection
 Commands in this group pass password as part of conList format, such as
 id=...,user=...,password=...
 These commands can drop password= altogether, and use only auth=, if
 both are provided, auth= takes precedence.

Group 2:
 * desktopLogin
 * discoverST
 Commands in this group receive password as a mandatory  argument, at
 a known index, for example: [address] [user] [pass], to avoid breaking
 compatibility, password argument has to be specified, even when using
 auth=, where auth= can come anywhere after all the mandatory arguments.
 For example: vdsClient someCommand 127.0.0.1 user - auth=method:...
 (note the '-')

Group 3:
 * setVmTicket
 auth=... can be passed only after '--' parameter, to avoid collision
 with the fifth optional parameter
 For example:
 vdsClient setVmTicket 127.0.0.1 user - disconnect -- auth=method:...

Bug-Url: https://bugzilla.redhat.com/1032525
Change-Id: I363a16e6a7872ca05e19d5f520bdba90fb492374
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>
Signed-off-by: Dima Kuznetsov <dkuznets@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/24733
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>