Add variable MET_BIN_DIR to replace {MET_INSTALL_DIR}/bin in the code

[jprestop]

Describe the Problem

METplus wrappers scripts currently reference {MET_INSTALL_DIR}/bin, expecting the MET executables to be located in a "bin" directory. However, NCO has asked for the executables to be in an "exec" directory, so we need to make this modifiable for the user.

Expected Behavior

Replace {MET_INSTALL_DIR}/bin with MET_BIN_DIR throughout the code so that the user can change if necessary and the scripts will find the MET executables.

Environment

Describe your runtime environment:
*1. Machine: WCOSS mars/venus and surge/luna
*2. OS: Linux

To Reproduce

Describe the steps to reproduce the behavior:
*1. Install the MET software using the --bindir option to install in a location other than "bin"
*2. Install the METplus software
*3. Run a use case
*4. Find that METplus cannot find the MET executables

Relevant Deadlines

METplus-3.1 release

Funding Source

?

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Define Related Issue(s)

Consider the impact to the other METplus components.

• METplus, MET, METdb, METviewer, METexpress, METcalcpy, METplotpy

Bugfix Checklist

See the METplus Workflow for details.

• Complete the issue definition above.
• Fork this repository or create a branch of master_<Version>.
  Branch name: bugfix_502_create_configurable_bin_dir
• Fix the bug and test your changes.
• Add/update unit tests.
• Add/update documentation.
• Push local changes to GitHub.
• Submit a pull request to merge into master_<Version>.
  Pull request: bugfix <Issue Number> master_<Version> <Description>
• Iterate until the reviewer(s) accept and merge your changes.
• Delete your fork or branch.
• Complete the steps above to fix the bug on the develop branch.
  Branch name: bugfix_<Issue Number>_develop_<Description>
  Pull request: bugfix <Issue Number> develop <Description>
• Close this issue.