Update setuptools and pip to parse more metadata

The Ubuntu xenial-provided versions of setuptools and pip don't parse
all metadata present in Python packages, especially not the "minimum
required Python version" bit. More and more packages are using this
information to limit Python 3.5-support to older versions of their
packages. In this case, the problem was caused by the "zipp" package,
which is a very remote dependency of fusesoc.

Fixes #597

azure-pipelines.yml

@@ -31,6 +31,12 @@ jobs:
   # Installing six is a workaround for pip dependency resolution: six is already
   # installed as system package with a version below the required one.
   # Explicitly installing six through pip gets us a supported version.
+  #
+  # Updating pip and setuptools is required to have these tools properly parse
+  # Python-version metadata, which some packages uses to specify that an older
+  # version of a package must be used for a certain Python version. If that
+  # information is not read, pip installs the latest version, which then fails
+  # to run.
   - bash: |
       sudo apt-get install -y \
           python3 \
@@ -47,7 +53,8 @@ jobs:
           curl \
           libelf-dev \
           clang-format \
-        && sudo pip3 install -U six fusesoc
+        && sudo pip3 install -U setuptools pip six \
+        && sudo pip3 install -U fusesoc
     displayName: Install dependencies
 
   - bash: |