ansible: fix multiple register vars on Fedora

[richardlau]

Tasks registering variables in Ansible will alway set the variable
regardless of any when clause(s). This means if more than one task
registers the same variable, the last one "wins". Fix the bootstrap
role on Fedora by correctly registering has_libselinux in both
fedora30 and non-fedora30 cases.

Refs: #2531

Fixes this error:

TASK [bootstrap : install libselinux-python bindings] ******************************************************************************************************
fatal: [test-digitalocean-fedora30-x64-2]: FAILED! => {"msg": "The conditional check 'os in (\"fedora30\") and has_libselinux.rc == 1' failed. The error was: error while evaluating conditional (os in (\"fedora30\") and has_libselinux.rc == 1): 'dict object' has no attribute 'rc'\n\nThe error appears to be in '/home/rlau/sandbox/github/build/ansible/roles/bootstrap/tasks/partials/fedora.yml': line 35, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: install libselinux-python bindings\n  ^ here\n"}