Update global-requirements for psutil to 3.2.0

In order to run monasca-agent in environments using the musl libc
such as Alpine Linux, we need psutil>=3.2.0 due to an issue in the
old release [1].

[1]: giampaolo/psutil#664

Change-Id: I76570d36648cde2838982542bc4fa2b65d12715f

Author: Kaiyan Sheng

global-requirements.txt

@@ -165,7 +165,7 @@ Pillow>=2.4.0  # PIL License
 Pint>=0.5  # BSD
 pip>=7.1.0  # MIT
 PrettyTable>=0.7.1,<0.8  # BSD
-psutil>=3.0.1  # BSD
+psutil>=3.2.0  # BSD
 pyasn1  # BSD
 pyasn1-modules  # BSD
 pycadf>=1.1.0,!=2.0.0  # Apache-2.0