[manylinux2010] Reduce glibc rebuild cache size

2.5GB -> 1GB, should save resources on both local builds and travis-ci builds

Author: mayeut

docker/glibc/Dockerfile-i686

@@ -8,7 +8,8 @@ RUN sed -i 's/enabled=1/enabled=0/g' /etc/yum/pluginconf.d/fastestmirror.conf &&
     sed -i 's;^#baseurl=http://mirror;baseurl=https://vault;g' /etc/yum.repos.d/*.repo
 
 RUN echo "i386" > /etc/yum/vars/basearch
-RUN yum -y update && \
-    yum install -y util-linux-ng
+RUN yum install -y util-linux-ng && \
+    yum -y clean all && \
+    rm -rf /var/cache/yum/*
 COPY ./build_scripts /build_scripts
 RUN linux32 bash /build_scripts/rebuild-glibc-without-vsyscall.sh

docker/glibc/build_scripts/rebuild-glibc-without-vsyscall.sh

@@ -52,4 +52,7 @@ mv $SRPM_TOPDIR/RPMS/* /rpms/
 # Show us what happened last before cleaning up the log
 echo ~~~~~~~~~~~~~~~~~~~~~ final lines of the build log ~~~~~~~~~~~~~~~~~~~~~ >/dev/null
 tail -n30 /var/log/build.log
-rm /var/log/build.log
+
+# We don't need to keep anything execept /rpms/*
+rm -rf /root /tmp /var /sbin
+rm -rf /usr /lib*