Address panic in GetLDAPError, add fuzzer

[TomSellers]

This PR addresses a panic in the following line that occurs if response.Children[0].Value is nil.

ldap/v3/error.go

Line 213 in 539d8f5

resultCode := uint16(response.Children[0].Value.(int64))

This panic was original discovered when fuzzing our own code.

The PR:

• Adds check for nil to avoid the panic
• Refactors the tests so that a test corpus is created that can be used for both tests and a fuzzer. This will reduce the boilerplate code needed when certain types of tests are added in the future.
• Adds a test for the issue fixed above
• Adds a fuzzer that is seeded by the corpus
• Updates the make fuzz command in Makefile to remove fuzzers that no longer exist and add the new one.

Misc other changes:

• Fixes an issue in Makefile that prevented podman from being used.
• Fixes an issue in TestExtendedRequest_FastBind where the test would error if the test target wasn't available. Since the error didn't stop the test a panic would be triggered when defer called conn.Close() on a nil conn.

Running the fuzzer with podman:

# prep env to pass pre-fuzz test run
podman machine start
make local-server

# run fuzzer
make fuzz

# to run w/o time constraint
(cd v3 && go test -v -fuzz  ^FuzzGetLDAPError$)

# teardown
stop-local-server
podman machine stop

[TomSellers]

This now matches the logic in TestExtendedRequest_WhoAmI above and ensures that the test doesn't panic due to calling conn.Close() on a nil conn if the test LDAP server isn't available.

[TomSellers]

In the prior code, the second shell was not being treated as a make keyword. This resulted in the podman check not working. The change here is to group the shell statements and pass them to shell.

[TomSellers]

Here and elsewhere below: All removed tests have been added to generateGetLDAPErrorCorpus.

[TomSellers]

Added a fix and test coverage for another panic shook out by the fuzzer added in this PR. I expected a panic here but didn't know how to replicate the invalid data.

[cpuschma]

Thank you for your PR and your work! Especially the fuzzing part is a nice addition

[TomSellers]

Thanks for the approval and comments @cpuschma
Do you have a sense for when this would be landed and released?

[cpuschma]

I'm planning to create a new release within approx. next week.