CP-7292 Pylint update

This is to update our pylint setup wrt the new CentOS 64 build environment.

Before merging them into sm repository, build.hg needs to update with extra dependency on the api target. This is because all our code depends on XenAPI.py (hence pylint depends its existence for checking). 

In the future, we should consider to move scripts like XenAPI.py outside of the api core component to facilitate finer grained dependency. In particular, with the SMAPI2 design, the SM's dependency should be merely the independent IDL instead.

```diff
diff --git a/b/config/sm.mk b/b/config/sm.mk
--- a/b/config/sm.mk
+++ b/b/config/sm.mk
@@ -1,7 +1,7 @@
 NAME ?= sm
 BUILD ?= yes
 CACHING ?= yes
-DEPENDS ?=  xen supp-pack-build
+DEPENDS ?=  xen api supp-pack-build
 REPOS ?= sm.git
 CHROOT ?= dom0
 EXTERNAL_BUILD ?= sm/mk/Makefile
```