[plugins/connection/switch] Use timeout from args rather than hard coded value

[wangxin]

Description of PR

Summary:
Fixes # (issue)

The connection plugin 'switch' uses hard coded timeout value 60s for
establishing SSH connection to target. After connection is spawned, then
the timeout value for matching expected output is set to value passed in
from keyword arguments.

In practice, sometimes the hard coded 60s timeout is not enough for
establishing SSH connection to targets. This improvement is to use value
passed in from keyword arguments for connection timeout. Since the
pexpect lib uses the same timeout value for establishing SSH connection
and matching expected output, there is no need to set timeout for
spawned connection in later code.

With this change, we can pass in a longer timeout value from arguments
when necessary.

Type of change

• Bug fix
• [] Testbed and Framework(new/improvement)
• [] Test case(new/improvement)

Approach

How did you do it?

Replace hard coded timeout values with value passed in from arguments. When no timeout argument is passed in, use default 60s.

How did you verify/test it?

Tested on Mellanox platform.

Any platform specific information?

No.

Supported testbed topology if it's a new test case?

Documentation

[lguohan]