Add reflectivity calculation back to WSM6 scheme

[weiwangncar]

TYPE: bug fix

KEYWORDS: radar reflectivity, WSM6

SOURCE: reported by Gabriel Cassol of Sigma Meteorologia, Brazil, internal

DESCRIPTION OF CHANGES:
Problem:
When moving WSM6 to MMM shared physics directory, the calculation of radar reflectivity was left out.

Solution:
The calculation of radar reflectivity is added back in the WSM6 scheme.

ISSUE: For use when this PR closes an issue.
Fixes #2096

LIST OF MODIFIED FILES:
M phys/module_mp_wsm6.F

TESTS CONDUCTED:

1. The reflectivity is computed now when namelist do_radar_ref is set to 1.
2. The Jenkins tests are all passing.

RELEASE NOTE: Fixed the bug of missing radar reflectivity in WSM6 scheme when do_radar_ref is set to 1.

[dudhia]

not seeing if Jenkins tests were done

[weiwangncar]

@dudhia As you can see I have been trying to start the tests a few times, but so far no success. Not sure what's going on.

[weiwangncar]

The Jenkins test results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None

[weiwangncar]

@dudhia @smileMchen Ready to be reviewed and approved.