Split buildPythonPackage into setup hooks

This commit splits the `buildPythonPackage` into multiple setup hooks.

Generally, Python packages are built from source to wheels using `setuptools`.
The wheels are then installed with `pip`. Tests were often called with
`python setup.py test` but this is less common nowadays. Most projects
now use a different entry point for running tests, typically `pytest`
or `nosetests`.

Since the wheel format was introduced more tools were built to generate these,
e.g. `flit`. Since PEP 517 is provisionally accepted, defining a build-system
independent format (`pyproject.toml`), `pip` can now use that format to
execute the correct build-system.

In the past I've added support for PEP 517 (`pyproject`) to the Python
builder, resulting in a now rather large builder. Furthermore, it was not possible
to reuse components elsewhere. Therefore, the builder is now split into multiple
setup hooks.

The `setuptoolsCheckHook` is included now by default but in time it should
be removed from `buildPythonPackage` to make it easier to use another hook
(curently one has to pass in `dontUseSetuptoolsCheck`).

pkgs/development/interpreters/python/hooks/pytest-check-hook.sh

@@ -0,0 +1,49 @@
+# Setup hook for pytest
+echo "Sourcing pytest-check-hook"
+
+declare -ar disabledTests
+
+function _concatSep {
+    local result
+    local sep="$1"
+    local -n arr=$2
+    for index in ${!arr[*]}; do
+        if [ $index -eq 0 ]; then
+            result="${arr[index]}"
+        else
+            result+=" $sep ${arr[index]}"
+        fi
+    done
+    echo "$result"
+}
+
+function _pytestComputeDisabledTestsString () {
+    declare -a tests
+    local tests=($1)
+    local prefix="not "
+    prefixed=( "${tests[@]/#/$prefix}" )
+    result=$(_concatSep "and" prefixed)
+    echo "$result"
+}
+
+function pytestCheckPhase() {
+    echo "Executing pytestCheckPhase"
+    runHook preCheck
+
+    # Compose arguments
+    args=" -m pytest"
+    if [ -n "$disabledTests" ]; then
+        disabledTestsString=$(_pytestComputeDisabledTestsString "${disabledTests[@]}")
+      args+=" -k \""$disabledTestsString"\""
+    fi
+    args+=" ${pytestFlagsArray[@]}"
+    eval "@pythonCheckInterpreter@ $args"
+
+    runHook postCheck
+    echo "Finished executing pytestCheckPhase"
+}
+
+if [ -z "$dontUsePytestCheck" ] && [ -z "$installCheckPhase" ]; then
+    echo "Using pytestCheckPhase"
+    preDistPhases+=" pytestCheckPhase"
+fi