Try to make the manylinux pip cache work.

On travis, it's complaining that: WARNING: The directory '/cache/pip' or its parent directory is not owned or is not writable by the current user. The cache has been disabled. Check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.

.travis.yml

@@ -266,7 +266,11 @@ jobs:
       env: DOCKER_IMAGE=quay.io/pypa/manylinux2010_x86_64
       install: docker pull $DOCKER_IMAGE
       script: bash scripts/releases/make-manylinux
-      before_script: python -mpip install -U pip twine
+      before_script:
+        - python -mpip install -U pip twine
+        - chmod a+w $HOME/.cache
+        - mkdir -p $HOME/.cache/pip
+        - chmod a+w $HOME/.cache/pip
 
     - stage: test
       name: 32-bit manylinux wheels (all Pythons)
@@ -275,7 +279,11 @@ jobs:
       env: DOCKER_IMAGE=quay.io/pypa/manylinux2010_i686 PRE_CMD=linux32
       install: docker pull $DOCKER_IMAGE
       script: bash scripts/releases/make-manylinux
-      before_script: python -mpip install -U pip twine
+      before_script:
+        - python -mpip install -U pip twine
+        - chmod a+rwx $HOME/.cache
+        - mkdir -p $HOME/.cache/pip
+        - chmod a+rwx $HOME/.cache/pip
 
     # Lint the code. Because this is a separate job, even if it fails fast
     # the tests will still run. Put it at the top for fast feedback.

scripts/releases/make-manylinux

@@ -93,7 +93,7 @@ echo Setting up caching
 python --version
 python -mpip --version
 LCACHE="$(dirname `python -mpip cache dir`)"
-echo Sharing pip cache at $LCACHE
+echo Sharing pip cache at $LCACHE $(ls -ld $LCACHE)
 echo Sharing ccache dir at $HOME/.ccache
 if [ ! -d $HOME/.ccache ]; then
     mkdir $HOME/.ccache