Find the path to the mongod executable for many-collection-test

Issue:

After having a closer look at the log file(v4.4) for the many-coll-test, I discovered that even though the task exited successfully, the test had not run. The reason is that it was unable to find the mongod executable.

The test runs successfully on develop and mongodb-5.0 as it is able to find the mongod executable.

Scope:

• Implement a better solution to WT-8796.
• Find the correct path to mongod executable.