Update rt_single function in rt.sh to parse correct .conf file

[DusanJovic-NOAA]

Description

Running single test from non-default .conf file does not work as expected, it always reads rt.conf instead of config file specified by -l flag. This PR updates rt_single function in rt.sh to use .conf if one is specified on command line using -l flag.

Input data additions/changes

• No changes are expected to input data.
• There will be new input data.
• Input data will be updated.

Anticipated changes to regression tests:

• No changes are expected to any regression test.
• Changes are expected to the following tests:

Subcomponents involved:

• AQM
• CDEPS
• CICE
• CMEPS
• CMakeModules
• FV3
• GOCART
• HYCOM
• MOM6
• NOAHMP
• WW3
• stochastic_physics
• none

Commit Queue Checklist:

• Link PR's from all sub-components involved
• Confirm reviews completed in sub-component PR's
• Add all appropriate labels to this PR.
• Run full RT suite on either Hera/Cheyenne with both Intel/GNU compilers
• Add list of any failed regression tests to "Anticipated changes to regression tests" section.

Linked PR's and Issues:

#1557
#1416

Testing Day Checklist:

• This PR is up-to-date with the top of all sub-component repositories except for those sub-components which are the subject of this PR.
• Move new/updated input data on RDHPCS Hera and propagate input data changes to all supported systems.

Testing Log (for CM's):

• RDHPCS
  • Intel
    • Hera
    • Orion
    • Jet
    • Gaea
    • Cheyenne
  • GNU
    • Hera
    • Cheyenne
• WCOSS2
  • Dogwood/Cactus
  • Acorn
• CI
  • Completed
• opnReqTest
  • N/A
  • Log attached to comment

[github-actions]

@DusanJovic-NOAA please bring these up to date with respective authoritative repositories

• ufs-weather-model NOT up to date
• fv3 NOT up to date

[jkbk2004]

@DusanJovic-NOAA I think we can combine this pr to Sam's #1554. Can we coordinate with Sam? Once we merge in #1560, then we can try to commit #1554 today.

[DusanJovic-NOAA]

Yes, this PR can be combined with #1554

[jkbk2004]

merged with #1554