Provide a config option to customize remote shell command

Our remote ssh code makes all kinds of assumptions about the shell and
path of the guest. Recently some code was added to the command to generate
errors more promptly but it does not work if the shell is /bin/sh. This
commit allows the user to configure tempest with a desired prologue to handle
this case. It does nothing to solve the more general problem and, like the
other image-related options, cannot be customized individually for various
images that tempest may use.

Debug logging of remote commands was also added.

Change-Id: I669dd4386ffb539dad88a9487bef6c172b5d65fa
Closes-Bug: #1465682

etc/tempest.conf.sample

@@ -254,6 +254,10 @@
 # value)
 #build_timeout = 300
 
+# Shell fragments to use before executing a command when sshing to a
+# guest. (string value)
+#ssh_shell_prologue = set -eu -o pipefail; PATH=$$PATH:/sbin;
+
 # Auth method used for authenticate to the instance. Valid choices
 # are: keypair, configured, adminpass and disabled. Keypair: start the
 # servers with a ssh keypair. Configured: use the configured user and

tempest/common/utils/linux/remote_client.py

@@ -14,6 +14,7 @@ import netaddr
 import re
 import time
 
+from oslo_log import log as logging
 import six
 from tempest_lib.common import ssh
 
@@ -22,6 +23,8 @@ from tempest import exceptions
 
 CONF = config.CONF
 
+LOG = logging.getLogger(__name__)
+
 
 class RemoteClient(object):
 
@@ -48,7 +51,8 @@ class RemoteClient(object):
     def exec_command(self, cmd):
         # Shell options below add more clearness on failures,
         # path is extended for some non-cirros guest oses (centos7)
-        cmd = "set -eu -o pipefail; PATH=$PATH:/sbin; " + cmd
+        cmd = CONF.compute.ssh_shell_prologue + " " + cmd
+        LOG.debug("Remote command: %s" % cmd)
         return self.ssh_client.exec_command(cmd)
 
     def validate_authentication(self):

tempest/config.py

@@ -206,6 +206,10 @@ ComputeGroup = [
                help="Timeout in seconds to wait for an instance to build. "
                     "Other services that do not define build_timeout will "
                     "inherit this value."),
+    cfg.StrOpt('ssh_shell_prologue',
+               default="set -eu -o pipefail; PATH=$$PATH:/sbin;",
+               help="Shell fragments to use before executing a command "
+                    "when sshing to a guest."),
     cfg.StrOpt('ssh_auth_method',
                default='keypair',
                help="Auth method used for authenticate to the instance. "