Make build script more robust (#96)

No guarantee that `pip` alias is set up correctly. Rely on `python3 -m`
command.

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scripts/build_and_install_distro.sh

@@ -14,7 +14,7 @@ if [ "$current_dir" != "aws-otel-python-instrumentation" ]; then
 fi
 
 # Setup - update dependencies and create/empty dist dir
-pip install --upgrade pip setuptools wheel packaging build
+python3 -m pip install --upgrade pip setuptools wheel packaging build
 mkdir -p dist
 rm -rf dist/aws_opentelemetry_distro*
 
@@ -25,5 +25,5 @@ python3 -m build --outdir ../dist
 # Install distro
 cd ../dist
 DISTRO=(aws_opentelemetry_distro-*-py3-none-any.whl)
-pip install $DISTRO --force-reinstall
+python3 -m pip install $DISTRO --force-reinstall
 cd ..