Refactor getPort to only check required port

[Cartmanishere]

Portfinder library gets port as follows --

1. getPort({:port 0}):

   • Returns a random port.

2. getPort({:port <non-zero>}):

   • Returns the first open port between <non-zero> and upper limit (which is 40000)

3. getPort({:port <lower-limit>, :stopPort <upper-limit>})

   • Returns a first open port between the range <lower-limit> and <upper-limit>

In the ember script, we should only check for the specified port and not check for a range.
Hence, for a non-zero required port, we check for an open port in the range -- [portNum, portNum]
So if this port is not available, then getPort will give an exception.

If the requested port is less than 1024, then the reason for port being unavailable can be that --

• Port is already in use
• You do not have sufficient permissions available

So we set appropriate error message based on the requested port.

[rwjblue]

Generally seems good to me, has some linting issues to clean up.

[Cartmanishere]

Fixed the linting issues. Thanks.

[rwjblue]

Thank you!