ipatests: fix the disable_dnssec_validation method

[flo-renaud]

Bind configuration now includes 2 snippet config files, in
/etc/named/ipa-ext.conf and /etc/named/ipa-options-ext.conf

When a test needs to disable dnssec-validation, it needs to edit
the snippet ipa-options-ext.conf instead of /etc/named.conf.

This commit fixes the method tasks.disable_dnssec_validation so that it
correctly updates the snippet.

Fixes: https://pagure.io/freeipa/issue/8364

[flo-renaud]

• test_smb issues are known failures: 8184 and 8344
• test_sssd issue is a known failure: 8294
• test_trust issue is a known failure: 8365
  The tests show that ipa trust-add command is now working, the failures happen after this step.

[abbra]

Linting issues:

2020-06-10T14:27:22.8729694Z pylint
2020-06-10T14:27:22.8731171Z ------
2020-06-10T14:27:30.4404108Z �[7;33m************* Module ipatests.pytest_ipa.integration.tasks�[0m
2020-06-10T14:27:30.4409849Z ipatests/pytest_ipa/integration/tasks.py:537: [E1101(�[1;31mno-member�[0m), disable_dnssec_validation] �[1;31mInstance of 'BasePathNamespace' has no 'NAMED_CUSTOM_OPTIONS_CONFIG' member�[0m)
2020-06-10T14:27:30.4411884Z ipatests/pytest_ipa/integration/tasks.py:538: [E1101(�[1;31mno-member�[0m), disable_dnssec_validation] �[1;31mInstance of 'BasePathNamespace' has no 'NAMED_CUSTOM_OPTIONS_CONFIG' member�[0m)
2020-06-10T14:27:30.4413024Z ipatests/pytest_ipa/integration/tasks.py:541: [E1101(�[1;31mno-member�[0m), disable_dnssec_validation] �[1;31mInstance of 'BasePathNamespace' has no 'NAMED_CUSTOM_OPTIONS_CONFIG' member�[0m)
2020-06-10T14:27:30.4413552Z 
2

[abbra]

Removed ack due to linting issues.

[flo-renaud]

@abbra
the lint issues have been fixed

[flo-renaud]

master:

• 1487665 ipatests: fix the disable_dnssec_validation method