[FVT]:support xcat-inventory on rhels7.6

[tingtli]

Install xcat-inventory on rhels7.6 x and get following errors

[root@c910f04x12v02 testcase]# xcat-inventory -V
Traceback (most recent call last):
  File "/opt/xcat/bin/xcat-inventory", line 11, in <module>
    from xcclient.inventory.shell import main
  File "/opt/xcat/lib/python/xcclient/inventory/shell.py", line 22, in <module>
    import xcclient.inventory.manager as mgr
  File "/opt/xcat/lib/python/xcclient/inventory/manager.py", line 10, in <module>
    from dbfactory import dbfactory
  File "/opt/xcat/lib/python/xcclient/inventory/dbfactory.py", line 3, in <module>
    import dbobject
  File "/opt/xcat/lib/python/xcclient/inventory/dbobject.py", line 44, in <module>
    class passwd(Base,mixin):
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/ext/declarative/api.py", line 55, in __init__
    _as_declarative(cls, classname, cls.__dict__)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 254, in _as_declarative
    **table_kw)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/sql/schema.py", line 406, in __new__
    table._init(name, metadata, *args, **kw)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/sql/schema.py", line 479, in _init
    self._autoload(metadata, autoload_with, include_columns)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/sql/schema.py", line 503, in _autoload
    self, include_columns, exclude_columns
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 1731, in run_callable
    with self.contextual_connect() as conn:
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 1798, in contextual_connect
    self.pool.connect(),
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 338, in connect
    return _ConnectionFairy._checkout(self)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 644, in _checkout
    fairy = _ConnectionRecord.checkout(pool)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 440, in checkout
    rec = pool._do_get()
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 963, in _do_get
    return self._create_connection()
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 285, in _create_connection
    return _ConnectionRecord(self)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 416, in __init__
    exec_once(self.connection, self)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/event/attr.py", line 250, in exec_once
    self(*args, **kw)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/event/attr.py", line 260, in __call__
    fn(*args, **kw)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 1219, in go
    return once_fn(*arg, **kw)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/strategies.py", line 166, in first_connect
    dialect.initialize(c)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/dialects/mysql/base.py", line 2453, in initialize
    self._detect_ansiquotes(connection)
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/dialects/mysql/base.py", line 2724, in _detect_ansiquotes
    mode = row[1] or ''
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/dialects/mysql/base.py", line 3226, in __getitem__
    return item.decode(self.charset)
LookupError: unknown encoding: utf8mb4```