[Doctest] add installation doctest (#1179)

### What this PR does / why we need it?
Install doctest

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
CI passed

Related: https://github.com/vllm-project/vllm-ascend/pull/983

Co-authored-by: wangli <wangli858794774@gmail.com>

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>
Co-authored-by: wangli <wangli858794774@gmail.com>

tests/e2e/run_doctests.sh

@@ -21,7 +21,13 @@ set -eo errexit
 
 . $(dirname "$0")/common.sh
 
+export VLLM_USE_MODELSCOPE=true
+export VLLM_LOGGING_LEVEL=ERROR
+
 _info "====> Start Quickstart test"
 . "${SCRIPT_DIR}/doctests/001-quickstart-test.sh"
 
+_info "====> Start pip binary installation test"
+. "${SCRIPT_DIR}/doctests/002-pip-binary-installation-test.sh"
+
 _info "Doctest passed."