Improve issue creation when moving to snapshots during the milestone and RC phases

[wilkinsona]

Right now, Bomr figures out the version by simply removing the -SNAPSHOT suffix. This works fine for patch releases where, for example, 1.2.3-SNAPSHOT will become 1.2.3. However, it doesn't work during the milestone and RC phases where, for example, 1.2.0-SNAPSHOT that's leading up to 1.2.0-M1, will become 1.2.0. It needs to become 1.2.0-M1 instead. To address this, we'll need to look at the schedule releases, figure out what the upcoming milestone or RC is, and use that instead.