Support summary written to HDFS

[372046933]

This PR supports use case below:

from mxboard import SummaryWriter
with SummaryWriter(logdir='hdfs://hdfs-nn-proxy-ns1/department/ai/user/xyz/logs') as sw:
    for i in range(10):
        # create a normal distribution with fixed mean and decreasing std
        data = mx.nd.normal(loc=0, scale=10.0/(i+1), shape=(10, 3, 8, 8))
        sw.add_histogram(tag='norml_dist', values=data, bins=200, global_step=i)