Create and publish filesystem images for Android builds

[danilo, 2012-07-20] Schedule for next month.
[danilo, 2012-07-23] This should be done against existing android-build.l.o, not against the new CI dashboard.
[pfalcon 2012-08-07] l-a-m-c commands to use are given at https://wiki.linaro.org/Platform/Android/ImageInstallation . They pretty much use only mandatory params and defaults for the rest. Default image size created is 2Gb. Trying to override that to 1Gb leads to error, i.e. not enough room, 1.5Gb works. Apparently, makes sense to use default value, but allow to override it in build config. An FS image bzip2 -9'es to 160Mb, so as expected, having FS images output will double storage requirements. So again, makes sense to enable/disable on via build config, and later think of default.
[pfalcon 2012-08-07] Successful build: https://android-build.linaro.org/builds/~pfalcon/panda-ics-gcc47-tilt-tracking-blob-lit/#build=10
[pfalcon 2012-08-13] Documented at https://wiki.linaro.org/Platform/Android/LinaroAndroidBuildService#Build_variables_for_BUILD_TYPE.3Dbuild-android

Meta:
Headline: Filesystem images provided for Android builds, to facilitate testing and streamlined deployment.
Acceptance: Any build can be configured to produce FS images alongside usual tarball artifacts.

Work items:
Decide on overall image size/partition structure: DONE
Provide linaro-android-media-create command to produce an image: DONE
Configure build slave to allow linaro-android-media-create be run under sudo to create an image: DONE
Validate image creation on test builds: DONE
Deploy image creation feature for all builds: DONE
Document image creation feature: DONE