replace os.popen with subprocess.Popen

Replace os.popen with subprocess.Popen since the older function would
fail (more or less) silently if the executed program cannot be found

There is a bb.process.run() which will invoke the Popen to run command,
use it for simplify the code.

For the:
p4file = os.popen("%s%s files %s" % (p4cmd, p4opt, depot))
...
for file in p4file:
    list = file.split()

in bitbake/lib/bb/fetch2/perforce.py, it should be an error in the past,
since it didn't use readline() to read the pipe, but directly used the
split() for the pipe. Use the bb.process.run would fix the problem since
bb.process.run will return strings.

More info:
http://docs.python.org/library/subprocess.html#subprocess-replacements

[YOCTO #2075]

(Bitbake rev: 8d6700255a6d4dda403c89b171a6d4a1883e5aae)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/fetch2/perforce.py

@@ -91,8 +91,8 @@ class Perforce(FetchMethod):
 
         p4cmd = data.getVar('FETCHCOMMAND_p4', d, True)
         logger.debug(1, "Running %s%s changes -m 1 %s", p4cmd, p4opt, depot)
-        p4file = os.popen("%s%s changes -m 1 %s" % (p4cmd, p4opt, depot))
-        cset = p4file.readline().strip()
+        p4file, errors = bb.process.run("%s%s changes -m 1 %s" % (p4cmd, p4opt, depot))
+        cset = p4file.strip()
         logger.debug(1, "READ %s", cset)
         if not cset:
             return -1
@@ -155,8 +155,8 @@ class Perforce(FetchMethod):
         logger.debug(2, "Fetch: creating temporary directory")
         bb.utils.mkdirhier(data.expand('${WORKDIR}', localdata))
         data.setVar('TMPBASE', data.expand('${WORKDIR}/oep4.XXXXXX', localdata), localdata)
-        tmppipe = os.popen(data.getVar('MKTEMPDIRCMD', localdata, True) or "false")
-        tmpfile = tmppipe.readline().strip()
+        tmpfile, errors = bb.process.run(data.getVar('MKTEMPDIRCMD', localdata, True) or "false")
+        tmpfile = tmpfile.strip()
         if not tmpfile:
             raise FetchError("Fetch: unable to create temporary directory.. make sure 'mktemp' is in the PATH.", loc)
 
@@ -169,7 +169,8 @@ class Perforce(FetchMethod):
         os.chdir(tmpfile)
         logger.info("Fetch " + loc)
         logger.info("%s%s files %s", p4cmd, p4opt, depot)
-        p4file = os.popen("%s%s files %s" % (p4cmd, p4opt, depot))
+        p4file, errors = bb.process.run("%s%s files %s" % (p4cmd, p4opt, depot))
+        p4file = p4file.strip()
 
         if not p4file:
             raise FetchError("Fetch: unable to get the P4 files from %s" % depot, loc)