ProcZoneInfoTest: Update parser for addition of high_min and high_max

Since f8780515fe91 ("mm: add pcp high_min high_max to proc zoneinfo")
2 new fields have been added to the /proc/zoneinfo cpu information -
high_min and high_max.

Update the parser to accept these and keep support for older kernels
without this patch.

Test: atest vts_kernel_proc_file_api_test
Bug: 398203082
Change-Id: Ifa7e2042da3094d0ed22db8589d40aeb095554be
Signed-off-by: Terence Tritton <ttritton@google.com>