Garbage Collector is not run in Coin

We do not run the garbage collector automatically, so we're in constant danger of running out of disk space. Last happened this morning.

Unpacking sources fails after enabling nightly builds with garbage collector:

agent:2017/05/30 13:16:12 build.go:343: Executing instruction 6 of 23
agent:2017/05/30 13:16:12 storageclient.go:381: Unpacking sources "/home/vmbuilder/ci-working-dir/storage/qt/qtcanvas3d/c16fc5a2d8dbe1ba172347f67101027139af2cfd/sources_win.tar.gz" in "c:\Users\qt\work\qt\qtcanvas3d"
agent:2017/05/30 13:16:12 retry.go:24: Operation failed with an error: EOF
agent:2017/05/30 13:16:12 retry.go:25: Trying again (attempt: 1 ) after sleep of 5s seconds...
agent:2017/05/30 13:16:17 storageclient.go:381: Unpacking sources "/home/vmbuilder/ci-working-dir/storage/qt/qtcanvas3d/c16fc5a2d8dbe1ba172347f67101027139af2cfd/sources_win.tar.gz" in "c:\Users\qt\work\qt\qtcanvas3d"
agent:2017/05/30 13:16:17 retry.go:24: Operation failed with an error: EOF
agent:2017/05/30 13:16:17 retry.go:25: Trying again (attempt: 2 ) after sleep of 10s seconds...
agent:2017/05/30 13:16:27 storageclient.go:381: Unpacking sources "/home/vmbuilder/ci-working-dir/storage/qt/qtcanvas3d/c16fc5a2d8dbe1ba172347f67101027139af2cfd/sources_win.tar.gz" in "c:\Users\qt\work\qt\qtcanvas3d"
agent:2017/05/30 13:16:27 retry.go:24: Operation failed with an error: EOF
agent:2017/05/30 13:16:27 retry.go:25: Trying again (attempt: 3 ) after sleep of 15s seconds...
agent:2017/05/30 13:16:42 storageclient.go:381: Unpacking sources "/home/vmbuilder/ci-working-dir/storage/qt/qtcanvas3d/c16fc5a2d8dbe1ba172347f67101027139af2cfd/sources_win.tar.gz" in "c:\Users\qt\work\qt\qtcanvas3d"
agent:2017/05/30 13:16:42 retry.go:24: Operation failed with an error: EOF
agent:2017/05/30 13:16:42 retry.go:25: Trying again (attempt: 4 ) after sleep of 20s seconds...
agent:2017/05/30 13:17:02 storageclient.go:381: Unpacking sources "/home/vmbuilder/ci-working-dir/storage/qt/qtcanvas3d/c16fc5a2d8dbe1ba172347f67101027139af2cfd/sources_win.tar.gz" in "c:\Users\qt\work\qt\qtcanvas3d"
agent:2017/05/30 13:17:02 agent.go:165: Build failed
agent:2017/05/30 13:17:02 agent.go:120: ERROR building: EOF

Log:

https://testresults.qt.io/coin/logview/qt/qtcanvas3d/9c5686b6851fb903574ee4a404915c5da3c9c22b/WindowsWindows_7x86WindowsWindows_7x86Mingw53qtci-windows-7-x86-2-657433DebugAndRelease_Release_OpenGLDynamic_DisableTests/9a6ee9c520220b7d18c220f82e962111c3bf70eb/build_1496136686/buildlog.txt.gz

Similar problem with another Linux build:

http://ci-files01-hki.ci.local:8080/coin/logview/qt/tqtc-qmlcompiler/d00ae3468deeb412ea1a9cf0d21d41c9c0372527/LinuxOpenSuse_13_01x86_64LinuxOpenSuse_13_01x86_64GCCqtci-linux-OpenSuSE-13.01-x86_64-1db9baDeveloperBuild_NoPch/b6f1c5fc379c2534c837f4f3abfb084e0b346421/build_1496141942/buildlog.txt.gz