Update libbot, use new repo

[mwoehlke-kitware]

Update libbot to bring in RobotLocomotion/libbot2#2, which fixes the last remaining bits of #3231. This also switches us to the new repository which shares history with upstream. (The old repository was separately copied from the old subversion repository, and had the same content but not the same SHA's.)

Fixes #3231.

@david-german-tri for feature and platform review (due to having reviewed the libbot PR).

Note: the old submodule SHA (RobotLocomotion/libbot@6d932c813e6e) corresponds to RobotLocomotion/libbot2@807d17220dc6. The effective changes can be seen here.

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This change is 

[david-german-tri]

I don't think I understand how to use this. If I invoke lcm-spy, message details are as absent as ever. If I invoke bot-spy, I get:

~/drake/drake-distro/build$ ./install/bin/bot-spy
Checking /home/dgerman/drake/drake-distro/build/install/share/java
   Found /home/dgerman/drake/drake-distro/build/install/share/java/lcmtypes_bot2-core.jar
   Found /home/dgerman/drake/drake-distro/build/install/share/java/lcmtypes_bot2-frames.jar
   Found /home/dgerman/drake/drake-distro/build/install/share/java/lcmtypes_bot2-param.jar
   Found /home/dgerman/drake/drake-distro/build/install/share/java/lcmtypes_bot2-procman.jar
   Found /home/dgerman/drake/drake-distro/build/install/share/java/lcmtypes_drake.jar
   Found /home/dgerman/drake/drake-distro/build/install/share/java/lcmspy_plugins_bot2.jar
./install/bin/bot-spy: 15: exec: lcm-spy: not found

[david-german-tri]

Also, note #3231 (comment)

[mwoehlke-kitware]

lcm-spy needs to be in PATH

[david-german-tri]

lcm-spy needs to be in PATH

Yeah, OK. I suppose that's the right thing to do, and it works.

[david-german-tri]

Reviewed 2 of 2 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[david-german-tri]

I'll go ahead and merge this, then clean up the remaining #3231 hacks in automotive/.

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Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[david-german-tri]

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Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[david-german-tri]

-@ggould-tri

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Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[mwoehlke-kitware]

I'll go ahead and merge this, then clean up the remaining #3231 hacks in automotive/.

Thanks! I took a brief look at those last night, but it wasn't immediately obvious what to do about them, and it was late. (Particularly, it seems we would want to leverage knowledge of Drake's superbuild to make sure PATH is set.) I was going to take another look this morning, but if you have it covered, that's much appreciated.

[jwnimmer-tri]

Per f2f with David: the automotive_demo.py will soon (1-2 weeks) be Bazel-only per #4574, so it's not worth fixing its CMake superbuild integration.

[david-german-tri]

Particularly, it seems we would want to leverage knowledge of Drake's superbuild to make sure PATH is set.

Yeah. I was planning to glom DRAKE_INSTALL_BIN_DIR into the subprocess PATH env var, when @jwnimmer-tri suggested I just drop it instead. I'm writing it down here in case someone else has the same problem in the future.