Load Optimizer Variables

Load Optimizer Variables

In this PR,
 1. new property of adam optimizer, "laod_var" is added to set loading
    momentum variables
 2. update the read and save binary file
    using  ml::train::OptimizerType
 3. update read in layer_node to skip the optimizer variables if
    load_var is set as "false"
 4. is_laod_var() is added in optimizer_devel

**Self evaluation:**
1. Build test:	 [X]Passed [ ]Failed [ ]Skipped
2. Run test:	 [X]Passed [ ]Failed [ ]Skipped

Signed-off-by: jijoong.moon <jijoong.moon@samsung.com>