TPM 1.2 tests cannot be run due to missing tpm plug

[Kristin Chuang]

[steps]
1. install checkbox
$ sudo snap install checkbox-snappy --devmode --edge
2. install tpm1.2 tools
$ sudo snap install tpm --devmode
3. launch checkbox-snappy
$ sudo checkbox-snappy.test-runner
4. select TPM tests and run them

[expected]
TPM cases can be completed

[actual]
TPM cases fail with namespace error.

[details]
hyac109@localhost:~$ snap list
Name Version Rev Developer Notes
bluez 5.37-2 11 canonical -
checkbox-snappy 0.11~s16 72 ce-certification-qa devmode
core 16.04.1 628 canonical -
pc 16.04-0.8 9 canonical -
pc-kernel 4.4.0-45-4 37 canonical -
pulseaudio 8.0-2 x1 devmode
snapweb 0.21.2 24 canonical -
tpm 1.2-3 9 canonical devmode

[Kristin Chuang (kristinchuang)]

* Tried connecting checkbox-snappy with tpm, the following error will be shown:

hyac109@localhost:~$ sudo snap connect checkbox-snappy:tpm
error: cannot perform the following tasks:
- Connect checkbox-snappy:tpm to : (snap "checkbox-snappy" has no plug named "tpm")

--------------------
* Also executed snap interfaces and got following output:

hyac109@localhost:~$ snap interfaces
Slot Plug
:bluetooth-control -
:camera -
:dcdbas-control -
:docker-support -
:firewall-control -
:fuse-support -
:hardware-observe -
:home -
:kernel-module-control -
:locale-control -
:log-observe -
:lxd-support -
:mount-observe -
:network -
:network-bind -
:network-control -
:network-observe -
:network-setup-observe -
:opengl -
:ppp -
:process-control -
:removable-media -
:shutdown -
:snapd-control -
:system-observe -
:system-trace -
:time-control -
:timeserver-control -
:timezone-control -
:tpm -
- checkbox-snappy:pulseaudio
- checkbox-snappy:udisks2