ZTS: adjust zpool_import_012_pos timeout

When running in the CI the zpool_import_012_pos test case occasionally
takes longer than the maximum 600 seconds.  When this happens the test
case is considered to have failed but always completes a few minutes
latter.  Since the logs suggest nothing has actually failed this commit
increases timeout and removes the exception.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#11286

tests/runfiles/common.run

@@ -402,6 +402,7 @@ tests = ['zpool_import_001_pos', 'zpool_import_002_pos',
     'import_rewind_config_changed',
     'import_rewind_device_replaced']
 tags = ['functional', 'cli_root', 'zpool_import']
+timeout = 1200
 
 [tests/functional/cli_root/zpool_labelclear]
 tests = ['zpool_labelclear_active', 'zpool_labelclear_exported',