Support bors try arguments.

[reitermarkus]

Allow trying individual targets.

Closes #651.

[reitermarkus]

bors try --target dummy

[Emilgardis]

if only there was a way to actually debug events properly :/

[bors]

try

Build failed:

• conclusion

[Emilgardis]

bors try --target dummy_.*

[bors]

try

Build failed:

• conclusion

[reitermarkus]

bors try --target "dummy"

[reitermarkus]

bors try --target "dummy"

[bors]

try

Already running a review

[bors]

try

Build failed:

• conclusion

[reitermarkus]

bors try --target "dummy"

[reitermarkus]

bors try --target dummy_.*

[bors]

try

Already running a review

[bors]

try

Build failed:

• conclusion

[reitermarkus]

bors try-

[reitermarkus]

bors try --target dummy_.*

[bors]

try

Build failed:

• conclusion

[reitermarkus]

bors try --target dummy_.*

[Emilgardis]

failing on a non-matched target instead of trying to correct the matrix is what should be done imo. Don't think it's possible to do conditional matrices

[reitermarkus]

I'm not quite sure what you mean.

[reitermarkus]

bors try --target freebsd

[bors]

try

Already running a review

[reitermarkus]

bors try-

[bors]

try

Build succeeded:

• conclusion

[reitermarkus]

bors try

[bors]

try

Build succeeded:

• conclusion

[reitermarkus]

bors try

[bors]

try

Build failed:

• conclusion

[reitermarkus]

bors try

[bors]

try

Build succeeded:

• conclusion

[reitermarkus]

bors try

[bors]

try

Build succeeded:

• conclusion

[reitermarkus]

@Emilgardis, this should be good to go.

[Emilgardis]

r=me, small nit not related to the pr, can be done separately

[Emilgardis]

can you add 609 to the changelog also :)

[reitermarkus]

bors r+

[bors]

Build succeeded:

• conclusion