Add make clean in docker/build.sh

[luotao1]

fix #8075
As the elapsed time of teamcity is 36 min, make clean will not increase the elapsed time of teamcity.
.

[luotao1]

make clean后，boost会出现以下错误：

[14:23:39]	CMakeFiles/extern_boost.dir/build.make:88: recipe for target 'third_party/boost/src/extern_boost-stamp/extern_boost-download' failed
[14:23:39]	CMakeFiles/Makefile2:653: recipe for target 'CMakeFiles/extern_boost.dir/all' failed
[14:23:39]	make[2]: *** [third_party/boost/src/extern_boost-stamp/extern_boost-download] Error 8
[14:23:39]	make[1]: *** [CMakeFiles/extern_boost.dir/all] Error 2
[14:23:39]	make[1]: *** Waiting for unfinished jobs....

原因是build/third_party/boost/src/extern_boost-stamp下的文件被删了：

• make clean前

[extern_boost-stamp]  -> $ ls
extern_boost-build      extern_boost-done      extern_boost-install  extern_boost-patch
extern_boost-configure  extern_boost-download  extern_boost-mkdir    extern_boost-update

• make clean后

[lextern_boost-stamp] -> $ ls
extern_boost-done  extern_boost-mkdir

而下载的boost_1_41_0在make clean前后都不变。

[reyoung]

Excellent works