docker: Build in a clean directory

Currently we configure and build under "$QEMU_SRC/tests/docker" which is
dubious. Create a fixed directory (to be friendly to ccache) and change
to there before calling build_qemu.
Signed-off-by: NFam Zheng <famz@redhat.com>
Message-Id: <1475047892-11955-1-git-send-email-famz@redhat.com>

tests/docker/common.rc

@@ -11,6 +11,9 @@
 # or (at your option) any later version. See the COPYING file in
 # the top-level directory.
 
+BUILD_DIR=/var/tmp/qemu-build
+mkdir $BUILD_DIR
+
 requires()
 {
     for c in $@; do

tests/docker/test-clang

@@ -15,6 +15,8 @@
 
 requires clang
 
+cd "$BUILD_DIR"
+
 OPTS="--enable-debug --cxx=clang++ --cc=clang --host-cc=clang"
 # -fsanitize=undefined is broken on Fedora 23, skip it for now
 # See also: https://bugzilla.redhat.com/show_bug.cgi?id=1263834

tests/docker/test-full

@@ -13,5 +13,7 @@
 
 . common.rc
 
+cd "$BUILD_DIR"
+
 build_qemu
 make check $MAKEFLAGS

tests/docker/test-mingw

@@ -15,6 +15,8 @@
 
 requires mingw dtc
 
+cd "$BUILD_DIR"
+
 for prefix in x86_64-w64-mingw32- i686-w64-mingw32-; do
     TARGET_LIST=x86_64-softmmu,aarch64-softmmu \
         build_qemu --cross-prefix=$prefix \

tests/docker/test-quick

@@ -13,6 +13,8 @@
 
 . common.rc
 
+cd "$BUILD_DIR"
+
 DEF_TARGET_LIST="x86_64-softmmu,aarch64-softmmu"
 TARGET_LIST=${TARGET_LIST:-$DEF_TARGET_LIST} \
 build_qemu