add option to mask command

[s0rthak]

Hi,

This pull request adds an option in the samba-client constructor to mask command by passing maskCmd: true.
This flag defaults to false in order to not disturb any existing functionality.

I've tested it with a few error cases. Differences are shown below:

OS: Debian GNU/Linux 9 (stretch)
smbclient: Version 4.5.16-Debian

(1): Incorrect Network name:
maskCmd: false

Error: Command failed: smbclient -U 'some-username' -c 'dir ' //10.10.0.2/bad-dir-path '<some_password>' --max-protocol SMB3↵Domain=[...] OS=[] Server=[]↵tree connect failed: NT_STATUS_BAD_NETWORK_NAME↵Domain=[...] OS=[] Server=[]↵

maskCmd: true

Error: tree connect failed: NT_STATUS_BAD_NETWORK_NAME↵Domain=[...] OS=[] Server=[]↵

(2): Incorrect credentials
maskCmd: false

Error: Command failed: smbclient -U 'some-username' -c 'dir ' //10.10.0.2/test '<some_password>' --max-protocol SMB3↵session setup failed: NT_STATUS_LOGON_FAILURE↵

maskCmd: true

Error: session setup failed: NT_STATUS_LOGON_FAILURE↵

(3): smbclient not installed
maskCmd: false

Error: Command failed: smbclient -U 'Guest' -N -c 'mkdir test-directory' 
/bin/sh: smbclient: command not found
/bin/sh: smbclient: command not found

maskCmd: true

Error: /bin/sh: smbclient: command not found

I eagerly await any feedback on this PR. Thanks in advance!

Closes #32

[jakesjews]

thanks!