mk_test_case_guide parses multi-line description as a single line

when running mk_test_case_guide we discovered that there's a problem with formatting of the description field. The conversion to RST converts multi-line descriptions into single lines of RST without preserving the linebreaks. Because of this, this job

unit: template
template-resource: device
template-filter: device.category == 'DISK' and device.name != ''
template-unit: job
plugin: shell
category_id: com.canonical.plainbox::disk
id: disk/stats_{name}
flags: deprecated
user: root
estimated_duration: 10.0
command: disk_stats_test {name}
_summary: Disk statistics for {product_slug}
_description:
 This test checks disk stats, generates some activity and rechecks stats to
 verify they've changed. It also verifies that disks appear in the various
 files they're supposed to.
 .
 This test will inspect the following disk:
 .
     product name: {product_slug}
     sysfs path: {path}
     device node path: /dev/{name}

returns a description that looks like this:

disk/stats_{name}
 This test checks disk stats, generates some activity and rechecks stats to
 verify they've changed. It also verifies that disks appear in the various
 files they're supposed to. . This test will inspect the following disk: .
 product name: {product_slug} sysfs path: {path} device node path:
 /dev/{name}

I have a feeling the '.' chars exist to force formatting, and that's likely because of limitations elsewhere that are more frequently used then mk-test-case-guide, so we should look into fixing the parser here or figuring out how to enforce these line breaks into RST.