So that we consistently return the same value from lsb_release() across
all calls that use dry-run, the function now accepts a dry_run argument
(defaulting to False). This way, in dry-run mode, the caller does not
need to supply the path to a specific example file anymore.
lsb_release(dry_run=True) -> will load examples/lsb-release-focal
Having said that, the caller is still left with the possibility to
specify the example file by using the path argument:
lsb_release(path="example/lsb-release-impish")
The path and dry_run arguments are mutually exclusive: providing both
will result in a ValueError.
Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>