Misctls13fixes

[simo5]

Misc fixes to minor bugs uncovered while working on tlsfuzzer/tlsfuzzer#496

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This change is 

[tomato42]

Reviewed 1 of 1 files at r1, 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved

[tomato42]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @simo5)

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tlslite/keyexchange.py, line 233 at r1 (raw file):

                # handles negative test cases when we try to pass in
                # schemes that are not supported in TLS1.3
                hash_name = HashAlgorithm.toRepr(signatureAlg[0])

if it's behaviour that other code depends on, then we need a unit test to verify that it works

added unit tests with md5

[tomato42]

Reviewed 2 of 2 files at r3, 1 of 1 files at r4.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @simo5)

[tomato42]

ok, looks good, feel free to merge when CI passes

Reviewable status: complete! all files reviewed, all discussions resolved