Improve keytab/ccache support

[gpotter2]

• better support for Kerberos FAST in ccache format
• fix minor bugs with adding kerberos keytabs
• improve chosing of ticket when using SPNEGO.from_cli_ssp
• add remove_cred function
• improvements to LDAPHero to support signing independently of encryption
• fix SPNEGOSSP bug in the selection of the mechanisms

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 105 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.11%. Comparing base (c3c62ec) to head (6c6273b).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/modules/ldaphero.py	0.00%	43 Missing ⚠️
scapy/utils.py	11.36%	39 Missing ⚠️
scapy/modules/ticketer.py	86.25%	11 Missing ⚠️
scapy/layers/ldap.py	56.25%	7 Missing ⚠️
scapy/layers/kerberos.py	20.00%	4 Missing ⚠️
scapy/layers/spnego.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4935      +/-   ##
==========================================
- Coverage   80.69%   80.11%   -0.59%     
==========================================
  Files         370      370              
  Lines       91759    91917     +158     
==========================================
- Hits        74045    73638     -407     
- Misses      17714    18279     +565     

Files with missing lines	Coverage Δ
scapy/compat.py	91.30% <100.00%> (+0.67%)	⬆️
scapy/layers/smb.py	76.70% <ø> (ø)
scapy/layers/smbclient.py	74.38% <100.00%> (ø)
scapy/layers/spnego.py	83.79% <85.71%> (-0.05%)	⬇️
scapy/layers/kerberos.py	58.66% <20.00%> (+0.09%)	⬆️
scapy/layers/ldap.py	67.11% <56.25%> (+0.11%)	⬆️
scapy/modules/ticketer.py	46.01% <86.25%> (+4.37%)	⬆️
scapy/utils.py	72.25% <11.36%> (-1.24%)	⬇️
scapy/modules/ldaphero.py	0.00% <0.00%> (ø)

... and 19 files with indirect coverage changes

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