[lldb] Improve CPUInfo test predicate

[DavidSpickett]

Summary

Use a with block for reading the cpuinfo file.

When loading the file fails (or we're not on Linux)
return an empty string. Since all the callers are
going to do "x in self.getCPUInfo()".

lldb/packages/Python/lldbsuite/test/lldbtest.py

def isPPC64le(self):
             return True
         return False
 
     def getCPUInfo(self):
         triple = self.dbg.GetSelectedPlatform().GetTriple()
 
         # TODO other platforms, please implement this function
         if not re.match(".*-.*-linux", triple):
-            return False
+            return ""
 
         # Need to do something different for non-Linux/Android targets
         cpuinfo_path = self.getBuildArtifact("cpuinfo")
         if configuration.lldb_platform_name:
             self.runCmd('platform get-file "/proc/cpuinfo" ' + cpuinfo_path)
         else:
             cpuinfo_path = "/proc/cpuinfo"
 
         try:
-            f = open(cpuinfo_path, 'r')
+            with open(cpuinfo_path, 'r') as f:
                 cpuinfo = f.read()
-            f.close()
         except:
-            return False
+            return ""
 
         return cpuinfo
 
     def isAArch64SVE(self):
         return "sve" in self.getCPUInfo()
 
     def isAArch64MTE(self):
         return "mte" in self.getCPUInfo()